Methods and apparatus for actuating ships' rudders have a long history of development and have over the years produced a wide range of mechanisms directed to the task of controllably setting ships' rudder angles. One particularly successful approach is found in the family of Rapson-Slide mechanisms that basically convert rectilinear port/starboard motion produced by heavy thruster devices into arcuate movement directly coupled to the ship's rudder post by crosshead pin/slider/fork components. Due to the substantive forces involved in setting and maintaining rudder angles, especially as ship size has increased, and further due to the criticality of this ship's component to life and commerce, the evolution of steering mechanisms has been conservatively paced with primary emphasis placed on safe and reliable approaches. Thus, the Rapson-Slide mechanism has come into widespread usage because of its simple mechanical arrangement that lends itself readily to strong and reliable component fabrication and long service life.
The availability of such a proven mechanism coupled with the advances in hydraulic control systems of all types for powering the driving elements has led to a plateau in the evolution of ships' steering mechanisms. Descriptions of typical prior art approaches may be found in a number of U.S. patents. Illustrative teachings of pressurized liquid-operated ships' steering gear systems, including the use of a wide range of Rapson-Slide type of mechanisms, are found in U.S. Pat. Nos. 4,365,573 to Jamieson, 4,209,986 to Cunningham, and 4,408,555 to Aung. An even earlier teaching of a somewhat related simplified ship's steering gear mechanism is found in U.S. Pat. No. 2,748,613 to Guay. The most recent three of these patents show the use of four hydraulic cylinders arranged as two pairs in parallel, with each pair in opposition to one another to actuate compound crosshead assemblies, which have found widespread acceptability in recent years. The 1980 patent to Cunningham provides a fairly detailed description of the closed loop hydraulic control system used to actuate the apparatus, while all three disclosures stress the reliability and redundancy of their associated mechanical and hydraulic systems. The early (1956) patent to Guay discloses the use of a single pair of double acting fluid cylinders for driving a lever and slide mechanism, the two cylinders interconnected by a stationary guide member on one side of its slider block.
Present day steering gear systems have well addressed the requirements of safety, reliability, and long service life. The question of mechanical efficiency has not, however, received anywhere near as much active attention. The improvements embodied in the present invention admirably address the efficiency issues inherent in the Rapson-Slide mechanisms and provide significant benefits in this regard while retaining all of the desirable attributes of the basic device.